Zuul has hit a scenario where a git repo update was unable to talk to
gerrit via ssh because it had reached its per user connection limit [0].
This then led to some openstack job failing [1].
The default limit (which we were using) is 64 connection per user.
Apparently this is not quite enough for a busy zuul? Increase this by
50% up to 96.
[0] http://paste.openstack.org/show/754741/
[1] http://lists.openstack.org/pipermail/release-job-failures/2019-July/001193.html
Change-Id: Ibeca2208485608f3b61aa716184165342bfcc3c9
cb33dba40a